Apparatus for providing a pure hydrogen stream for use with fuel cells

ABSTRACT

An apparatus is provided which comprises two burner zones using a single igniter separated by a heat transfer zone for use in low-cost hydrogen generation units. When used in conjunction with a control system which limits the effluent temperature to less than about 700° C., the apparatus can be constructed of materials such as carbon steel and stainless steel rather than more exotic materials. This simplified structure and the use of less exotic materials provides an efficient, low-cost combined partial oxidation reactor for small-scale hydrogen production systems, especially for hydrogen production systems associated with fuel cell operation for the production of electricity.

FIELD OF THE INVENTION

The present invention relates to a hydrogen generating apparatus and,more particularly, to a hybrid reforming reactor which is suitable foruse as a hydrogen generation system or as an electric power generationsystem when used in conjunction with a fuel cell.

BACKGROUND OF THE INVENTION

The use of fuel cells to generate electrical power for electricity or todrive a transportation vehicle relies upon the generation of hydrogen.Because hydrogen is difficult to store and distribute, and becausehydrogen has a low volumetric energy density compared to fuels such asgasoline, hydrogen for use in fuel cells will have to be produced at apoint near the fuel cell, rather than be produced in a centralizedrefining facility and distributed like gasoline. To be effective,hydrogen generation for fuel cells must be smaller, simpler, and lesscostly than hydrogen plants for the generation of industrial gasses.Furthermore, hydrogen generators for use with fuel cells will have to beintegrated with the operation of the fuel cell and be sufficientlyflexible enough to efficiently provide a varying amount of hydrogen asdemand for electric power from the fuel cell varies.

Hydrogen is widely produced for chemical and industrial purposes byconverting materials such as hydrocarbons and methanol in a reformingprocess to produce a synthesis gas. Such production usually takes placein large facilities which are rarely turned down in production for evena few days per year. In addition, the operation of the industrialhydrogen production facilities are often integrated with associatedfacilities to improve the use of energy for the overall complex.Synthesis gas is the name generally given to a gaseous mixtureprincipally comprising carbon monoxide and hydrogen, but also possiblycontaining carbon dioxide and minor amounts of methane and nitrogen. Itis used, or is potentially useful, as feedstock in a variety oflarge-scale chemical processes, for example: the production of methanol,the production of gasoline boiling range hydrocarbons by theFischer-Tropsch process and the production of ammonia.

Processes for the production of synthesis gas are well known andgenerally comprise steam reforming, autothermal reforming, non-catalyticpartial oxidation of light hydrocarbons or non-catalytic partialoxidation of any hydrocarbons. Of these methods, steam reforming isgenerally used to produce synthesis gas for conversion into ammonia ormethanol. In such a process, molecules of hydrocarbons are broken downto produce a hydrogen-rich gas stream. A paper titled “Will DevelopingCountries Spur Fuel Cell Surge?” by Rajinder Singh, which appeared inthe March 1999 issue of Chemical Engineering Progress, page 59-66,presents a discussion of the developments of the fuel cell and methodsfor producing hydrogen for use with fuel cells. The article particularlypoints out that the partial oxidation process is a fast processpermitting small reactors, fast startup, and rapid response to changesin the load, while steam reforming is a slow process requiring a largereactor and long response times, but operates at a high thermalefficiency. The article highlights one hybrid process which combinespartial oxidation and steam reforming in a single reaction zone asdisclosed in U.S. Pat. No. 4,522,894.

Modifications of the simple steam reforming processes have been proposedto improve the operation of the steam reforming process. In particular,there have been suggestions for improving the energy efficiency of suchprocesses in which the heat available from the products of a secondaryreforming step is utilized for other purposes within the synthesis gasproduction process. For example, processes are described in U.S. Pat.No. 4,479,925 in which heat from the products of a secondary reformer isused to provide heat to a primary reformer.

The reforming reaction is expressed by the following formula:

CH₄+2H₂O→4 H₂+CO₂

where the reaction in the reformer and the reaction in the shiftconverter are respectively expressed by the following simplifiedformulae (1) and (2):

CH₄+H₂O→CO+3 H₂  (1)

CO+H₂O→H₂+CO₂  (2)

In the water gas shift converter which typically follows a reformingstep, formula (2) is representative of the major reaction.

U.S. Pat. No. 4,925,456 discloses a process and an apparatus for theproduction of synthesis gas which employs a plurality of double pipeheat exchangers for primary reforming in a combined primary andsecondary reforming process. The primary reforming zone comprises atleast one double-pipe heat exchanger-reactor and the primary reformingcatalyst is positioned either in the central core or in the annulusthereof. The invention is further characterized in that the secondaryreformer effluent is passed through which ever of the central core orthe annulus is not containing the primary reforming catalystcountercurrently to the hydrocarbon-containing gas stream.

U.S. Pat. No. 5,181,937 discloses a system for steam reforming ofhydrocarbons into a hydrogen rich gas which comprises a convectivereformer device. The convective reformer device comprises an outer shellenclosure for conveying a heating fluid uniformly to and from a coreassembly within the outer shell. The core assembly consists of amultiplicity of tubular conduits containing a solid catalyst forcontacting a feed mixture open to the path of the feed mixture flow suchthat the path of the feed mixture flow is separated from the heatingfluid flow in the outer shell. In the process, an autothermal reformerfully reforms the partially reformed (primary reformer) effluent fromthe core assembly and supplies heat to the core assembly by passing thefully reformed effluent through the outer shell of the convectivereforming device.

U.S. Pat. No. 5,595,833 discloses a process and apparatus for operatinga solid oxide fuel cell stack and includes an adiabatic pre-reformer toconvert about 5 to 20% of the hydrocarbon fuel into methane, hydrogen,and oxides of carbon At startup the pre-reformer is used to performpartial oxidation with methanol to heat the solid oxide fuel stack to atemperature of about 1000° C. When the temperature of the region of thepre-reformer reaches about 500° C. the methanol flow is terminated.

WO 97/45887 discloses a hydrodesulfurizer assembly which is thermallycoupled with process gas heat exchangers and a shift converter. Thehydrodesulfurizer assembly is employed to cool the reformer effluentprior to passing the cooled reformer effluent to the shift converterzone.

WO 98/13294 discloses a process for removing carbon monoxide from a gasstream by subjecting the gas stream to a first stage high temperatureselective catalytic methanation to lower the carbon monoxideconcentration, followed by a second stage low temperature selectivecatalytic methanation to further lower the residual carbon monoxideconcentration in the gas stream to a carbon monoxide concentration below40 ppm.

U.S. Pat. No. 4,943,493 discloses a fuel cell power plant whichintegrates the operation of a reformer to convert a hydrocarbon fuelinto a hydrogen-rich fuel which is passed to the anode side of a fuelcell. A portion of the anode exhaust stream is withdrawn from the fuelcell and passed to a burner zone wherein the anode exhaust gas stream ismixed with an oxidant stream and combusted to provide heat to thereformer. U.S. Pat. No. 4,943,493 discloses the problem of monitoringand controlling the flame temperature in the burner zone and claims anindirect approach to maintaining the flame temperature with a rangewhich results in complete combustion of the fuel and avoids a very highflame temperature which may exceed the temperature resistance of theburner liner materials. The reference discloses the control of thecomposition of the burner gas by bypassing a portion of the anode wastegas to maintain an adiabatic flame temperature between about 1150° C.(210020 F.) and about 1480° C. (2700° F.) whereby the heat transfer tothe reforming zone occurs in the radiant region to provide a highefficiency steam reforming operation.

U.S. Pat. No. 4,861,348 discloses a fuel reforming apparatus wherein theheat for the reforming zone is provided by a combustor. Flames formedwithin the combustion zone generate a high temperature combustion gas.The apparatus includes a heat-insulating layer for preventing radiationheat losses from the combustion gas, and a combustion gas passagedisposed around the reforming zone to permit combustion gas to flowtherethrough. A hydrocarbon/steam mixture is preheated by flowing on theoutside of the combustion gas passage in a supply passage before themixture is passed to the reforming zone. Heat insulation is provided asan outer layer disposed around the outer peripheral surface of thesupply passage to prevent the loss of radiation from the inner wall. Inone embodiment, reforming catalyst is disposed on the outside of thecombustion gas passage in the supply passage to extend the reformingzone.

U.S. Pat. No. 4,863,712 discloses a steam reforming process wherein ahydrocarbon feedstock, such as methane, natural gas, LPG, or naphtha isreacted with steam and/or carbon dioxide in the presence of a supportedcatalyst such as nickel or cobalt. The heat required for the endothermicreaction is supplied from the sensible heat of the reactants or from anexternal heat source. The reformer outlet is maintained in the range of700-900° C. or higher.

U.S. Pat. No. 4,869,894 discloses a process for the production andrecovery of high purity hydrogen. The process comprises reacting amethane-rich gas mixture in a primary reforming zone at a lowsteam-to-methane molar ratio of up to about 2.5 to produce a primaryreformate, followed by reacting the primary reformate in a secondaryreforming zone with oxygen to produce a secondary reformate, comprisinghydrogen and oxides of carbon. The secondary reformate is subjected to ahigh temperature water gas shift reaction to reduce the amount of carbonmonoxide in the hydrogen-rich product. The hydrogen-rich product iscooled and processed in a vacuum swing adsorption zone to remove carbondioxide and to produce a high purity hydrogen stream.

WO 98/08771 discloses an apparatus and method for converting feedstreams such as a hydrocarbon fuel or an alcohol into hydrogen andcarbon dioxide. The process comprises passing the feed stream first to apartial oxidation reaction zone to produce a partial oxidation effluent.The partial oxidation effluent is passed to a separate steam reformingreaction zone. The partial oxidation reaction zone and the steamreforming reaction zone are disposed in a first vessel. A helical tubeis extended about the first vessel and a second vessel is annularlydisposed about the first vessel such that the helical tube is disposedbetween the first and second vessels. The third vessel annularlydisposed around the second vessel. Oxygen is preheated in the helicaltube by heat from the partial oxidation reaction prior to being passedto the partial oxidation zone. The reformate from the steam reformingreaction zone is passed between the first and second vessel and issubjected to a high temperature shift reaction to reduce the carbonmonoxide content of the reformate stream. The thus treated reformatestream is desulfurized, cooled, and subjected to a low temperature shiftreaction.

U.S. Pat. No. 5,741,474 discloses a process for producing high purityhydrogen by reforming a hydrocarbon and/or oxygen atom containinghydrocarbon to form a reformed gas containing hydrogen, and passing thereformed gas through a hydrogen-separating membrane to selectivelyrecover hydrogen. The process comprises the steps of heating a reformingchamber, feeding the hydrocarbon along with air and/or steam to thechamber and therein causing both steam reforming and partial oxidationto take place to produce a reformed gas. The reformed gas is passedthrough a separating membrane to recover a high purity hydrogen streamand the non-permeate stream is combusted to provide heat to thereforming chamber.

U.S. Pat. No. 5,858,314 discloses a natural gas reformer comprising astack of catalyst plates supporting reforming catalyst and a pluralityof thermally conducting plates alternately stacked to form a reformingstructure, wherein the conductive plates transfer heat energy in-plane,across the surface of the conductive plate to support the reformingprocess.

Conventional steam reforming plants are able to achieve high efficiencythrough process integration; that is, by recovering heat from processstreams which require cooling. In the conventional large-scale plantthis occurs in large heat exchangers with high thermal efficiency andcomplex control schemes. In the present invention for the production ofhydrogen for fuel cells it is desired to reach a high degree of processintegration, with minimal equipment in order to reduce the size of theplants and the complexity of the control scheme. U.S. Pat. No. 5,861,441discloses a process that is representative of such an integratedprocessing scheme for large plants with integrated compression and heatexchange. It is the objective of this invention to provide a compactapparatus for generating hydrogen from available fuels such as naturalgas, hydrocarbons, and alcohols for use in a fuel cell to generateelectric power. One of the problems faced by developers of hydrogengenerators working with fuel cells for domestic and transportation useis the high cost of exotic material of construction which are requiredto withstand the high reaction temperatures of the partial oxidation andreforming processes. It is an objective of the present invention toprovide a hydrogen generator for converting natural gas to hydrogenwhich can be operated without exceeding a process temperature of 700° C.in the heat exchange equipment and thus can be constructed ofconventional materials.

Fuel cells are chemical power sources in which electrical power isgenerated in a chemical reaction. The most common fuel cell is based onthe chemical reaction between a reducing agent such as hydrogen and anoxidizing agent such as oxygen. The consumption of these agents isproportional to the power load. Polymers with high protonicconductivities are useful as proton exchange membranes (PEM's) in fuelcells. Among the earliest PEM's were sulfonated, crosslinkedpolystyrenes. More recently sulfonated fluorocarbon polymers have beenconsidered. Such PEM's are described in an article entitled, “NewHydrocarbon Proton Exchange Membranes Based on SulfonatedStyrene-Ethylene/Butylene-Styrene Triblock Copolymers”, by G. E. Wnek,J. N. Rider, J. M. Serpico, A. Einset, S. G. Ehrenberg, and L. Raboinpresented in the Electrochemical Society Proceedings (1995), Volume95-23, pages 247 to 251.

It is an objective of the present invention to solve some of theproblems associated with small-scale systems for producing hydrogen fora fuel cells, to provide simplified methods for producing hydrogen for afuel cell, to provide simple and efficient methods for controlling thehydrogen generation system associated with a fuel cell, and to providean apparatus for the generation of hydrogen that permits the reductionin scale of hydrogen generation facilities without a corresponding lossof efficiency. It is an objective of the present invention to provide aprocess for using the anode waste gas as the primary fuel for thegeneration of hydrogen for a fuel cell wherein the fluctuations in theanode waste gas flow rate and heating value are managed in the processto maintain a high overall energy efficiency.

It is an objective of this invention to provide an integrated fuel celland hydrogen production system which is energy and hydrogen efficient.More particularly, it is an objective of the present invention toprovide a process which starts up rapidly while operating at anefficiency level approaching that of a steam reformer operation.

It is an objective of the present invention to provide a process andapparatus for the generation of hydrogen for use in a fuel cell whichoffers a high degree of feed flexibility and which eliminates the use ofa separate external fuel.

It is an objective of the present invention to provide a process andapparatus which avoids thermal cycling of the heat transfer equipment ina hydrogen generator for a fuel cell for the generation of electricity.Thermal cycling in heat exchange and reactor equipment can have adeleterious effect on such equipment and result in premature equipmentfailure. In the operation of fuel cells the demand for electricity isgenerally not constant resulting in the turn-down of the hydrogengeneration equipment. Typically the turn-down ratios are very large inproportion to the daily fluctuation of demand for electric power. Inaddition, such systems often experience variation in the supply andquality of feeds and fuels consumed in the process which can impart athermal cycling of the heat exchange equipment. Such thermal cycling candamage welds which could compromise the safety of the operation of thehydrogen generation equipment.

SUMMARY OF THE INVENTION

The compact hydrogen generation process and apparatus of the presentinvention solves a number of problems of operating such hydrogenationproduction systems in conjunction with fuel cells for the generation ofelectric power. Integrated hydrogen generation and fuel cell systems togenerate electricity require meeting an electrical demand which isgenerally transient. Meeting these transient demands results intransient operation of the hydrogen generator which requires rapidstartup and sharp turndown of the generation of hydrogen, becausehydrogen cannot be stored. During the rapid startup or turndown, theheat exchange equipment can undergo thermal cycling. The presentinvention significantly eliminates thermal cycling while avoiding theuse of complex control schemes and exotic metallurgy to provide ahydrogen generation system integrated with a fuel cell. Furthermore, thefuel processor of the present invention is applicable to a wide varietyof fuel cell types including proton exchange membrane, solid oxide, andothers. The present invention can achieve overall energy efficiencies upto about 85% which are comparable to steam reforming without the slowstartup problems generally associated with steam reforming hydrogengenerators. The apparatus of the present invention can be used incombination with hydrogen purification equipment such as pressure swingadsorption, temperature swing adsorption, absorption, cryogenicdistillation, chemisorption, or membranes to provide high purityhydrogen for small commercial applications.

In one embodiment, the present invention is an combined partialoxidation burner reactor apparatus. The apparatus comprises a verticallyaligned reactor shell having a top head and a bottom head, and side-wallwhich define an interior reactor zone. The interior reactor zone has anupper shell zone, a center shell zone, and a lower shell zone. A hollowcenter sleeve is sealingly disposed on the top head and extendsdownwardly into the lower shell zone. The center sleeve has a hollowinterior which defines an upper core zone, a center core zone, and alower core zone. An intermediate partition which has a downwardlyconverging diameter along its length is sealingly disposed on the wallin the center shell zone encircling a portion of said hollow centersleeve. The lower core zone is in fluid communication with a portion ofthe center shell zone located within the partition. A burner zone isdefined within the interior reactor zone outside of the partition. Afeed inlet nozzle is disposed on said top head in fluid communicationwith the upper core zone. A product outlet nozzle is disposed on thereactor shell in fluid communication with the upper shell zone. A burnerfeed nozzle is disposed on the reactor shell in fluid communication withthe burner zone. An exhaust nozzle is disposed on the reactor shell influid communication with the burner zone. An igniter extends through thetop head and downwardly into the center core zone. A first oxidationcatalyst is disposed in the center core zone and a reforming catalyst isdisposed above the bottom of the partition in the center shell zone andin the lower core zone.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block flow diagram illustrating the core processof the performed by the apparatus.

FIG. 2 is a schematic block flow diagram illustrating pre and postprocessing options that may be used in conjunction with the apparatus ofthis invention.

FIG. 3 is a side view of a combined reaction zone apparatus of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

The process and apparatus of the current invention uses a hydrocarbonstream such as natural gas, liquefied petroleum gas (LPG), butanes,gasoline, oxygenates, biogas, or naphtha (a gasoline boiling rangematerial) as a feedstock. Natural gas and similar hydrocarbon streamsgenerally contain impurities such as sulfur in the form of hydrogensulfide, mercaptans, and sulfur oxides which must be removed prior tointroducing the feedstock to the steam reforming zone. The removal ofsulfur from the hydrocarbon feedstock may be accomplished by anyconventional means including adsorption, chemisorption, and catalyticdesulfurization. Generally, the type of pre-processing module for thehydrocarbon feedstock before it is charged to the fuel processor willdepend on the character or type of hydrocarbon feedstock. A natural gasstream will generally contain small amounts of sulfur as hydrogensulfide. Hydrogen sulfide in natural gas can be removed by contactingthe natural gas stream with a chemisorbent such as zinc oxide in a fixedbed desulfurization zone. LPG, which comprises propane, butane, ormixtures thereof, generally contains very little sulfur and can beprocessed directly by the fuel processor, although the use of a guardbed of containing an adsorbent or a chemisorbent to protect the catalystin the fuel processor may be included and some pressure moderatingdevice such as a valve is required to deliver the LPG to the fuelprocessor. The pre-processing module, or pre-processor for a naphthastream requires multi-stage treatment. Naphtha may have impurities suchas sulfur as mercaptan sulfur, chemically combined sulfur (such assulfides and disulfides), elemental sulfur, and hydrogen sulfide. Inorder to remove these sulfur impurities from the naphtha stream acombination of hydrodesulfurization in the presence of hydrogen over adesulfurization catalyst containing cobalt and molybdenum on a metaloxide base to convert the sulfur species to hydrogen sulfide, and asecond stage to remove the hydrogen sulfide are required. Although anyconventional hydrocarbon desulfurization catalyst may be used in thehydrodesulfurization zone, catalysts containing cobalt and molybdenumare preferred. In order to reduce the overall size of the hydrogengeneration equipment, chemisorption with a material such as zinc oxideis preferred for removal of hydrogen sulfide. The chemisorption orhydrodesulfurization based desulfurization operations will generallytake place at effective desulfurization conditions including adesulfurization pressure of between about 100 to about 1000 kPa.Preferably the desulfurization operation is carried out at adesulfurization pressure of between 200 and 300 kPa. Preferably thedesulfurization operation is carried out at a desulfurizationtemperature less than about 300° C., and more preferably thedesulfurization operation is carried out at a desulfurizationtemperature between about 50° C. and about 300° C. Preferably theconcentration of sulfur in the desulfurized feedstock will be less thanabout 10 ppm-wt, and more preferably the concentration of sulfur in thedesulfurized feedstock will be less than about 1 ppm-wt.

Water is required by the steam reforming process for use as a reactantand as a cooling medium. In addition for some types of fuel cells, thehydrogen product must be delivered to the fuel cell as a wet gas. Thisis particularly true with PEM fuel cells, wherein the humidity of thehydrogen product stream is controlled to avoid drying out the PEMmembrane in the fuel cell. The water used in the steam reforming processpreferably is deionized to remove dissolved metals and anions. Metalswhich could be harmful to catalysts include sodium, calcium, lead,copper, and arsenic. Anions such as chloride ions should be reduced orremoved from water. Removal of these cations and anions are required toprevent pre-mature deactivation of the steam reforming catalyst or othercatalytic materials contained in the fuel cell such as the water gasshift catalyst or the carbon monoxide oxidation catalyst in a carbonmonoxide reduction zone. The deionization of the water to be used in theprocess may be accomplished by any conventional means.

One of the problems addressed by the present invention is the supply ofheat to a steam reforming reaction which will convert hydrocarbon, oralcohol to hydrogen and oxides of carbon in the presence of water orsteam over a reforming catalyst. Alcohols and other oxygen-containinghydrocarbons are easier to reform and generally can be reformed atrelatively low reforming temperatures. However, hydrocarbons require ahigher heat input. Prior to the process of the present invention,attempts were made to transfer heat in the radiant and the convectionrange of heat transfer. Unfortunately, this requires the use of hightemperature radiant heat transfer zones and correspondingly exoticmetallurgy to provide sufficient heat to the reforming reaction at anacceptable heating rate. In the present scheme, the feedstock is firstpre-reformed at a moderate pre-reforming temperature of less than about700° C., and the pre-reformed effluent is subjected to a partialoxidation step. The heat generated in the exothermic partial oxidationstep can provide the heat to the endothermic reforming step if the twosteps occur in close proximity to each other, and independent of otherheat integration within the integrated process of hydrogen generationand fuel cell operation. In this manner the partial oxidation zone canprovide heat at high temperatures (i.e., greater than about 700° C.). Bythe use of the pre-reforming zone and the partial oxidation zone, it isbelieved that the reforming temperature can now be lowered from the hightemperature to a moderate temperature range (below about 700° C.) whereexotic metallurgy is not required, or to a range wherein a portion ofthe reforming reaction heat may be supplied by other heat sources withinthe overall process. Thus, by this rearrangement, the reforming stepbecomes independent of high temperature process heat integration and canbe operated either in the radiant or in the convection range in closeproximity to the partial oxidation reaction. The reforming reaction canalso take place without the use of exotic metallurgy. For example, theheat required by the pre-reforming step can be supplied by indirect heatexchange within the overall process. Heat required for the pre-reformingstep can be provided by heat from the exothermic water gas shiftreaction step, or heat for the reforming process can be provided by theheat of combustion of waste gases from the fuel cell, or a combinationthereof. Preferably, the heat for the pre-reforming step is supplied byindirect heat exchange with flue gases from the combustion of anodewaste gas from the fuel cell anode electrode.

The pre-processed feedstock is admixed with a steam stream to form apre-reforming admixture and the pre-reforming admixture is passed to apre-reforming zone for the partial conversion of the pre-treatedfeedstock to a pre-reformed stream comprising hydrogen, carbon monoxide,carbon dioxide, and unconverted hydrocarbons. The steam can be suppliedby the indirect heating of water with process heat from heat recoveredin the water gas shift reaction or from heat recovered from flue gasresulting from the combustion of anode waste gas. Preferably the steamis supplied by heating water with the heat recovered from the water gasshift reaction zone. Preferably, the steam to carbon ratio of thepre-reforming admixture is between about 1:1 and about 6:1, and morepreferably, the steam to carbon ratio of the pre-reforming admixture isbetween about 1:1 and about 3:1, and most preferably, the steam tocarbon ratio of the pre-reforming admixture comprises about 2:1. Thepre-reforming zone contains a pre-reforming catalyst comprising acatalyst base such as alumina with a metal deposited thereon.Preferably, the pre-reforming catalyst includes nickel with amounts ofnoble metal, such as cobalt, platinum, palladium, rhodium, ruthenium,iridium, and a support such as magnesia, magnesium aluminate, alumina,silica, zirconia, singly or in combination. More preferably, the steamreforming catalyst can be a single metal such as nickel or a noble metalsupported on a refractory carrier such as magnesia, magnesium aluminate,alumina, silica, or zirconia, singly or in combination, promoted by analkali metal such as potassium. The pre-reforming catalyst can begranular and is supported within the steam reforming zone. Thepre-reforming catalyst may be disposed in a fixed bed or disposed ontubes or plates within the pre-reforming zone. In the process of thepresent invention, the pre-reforming zone is operated at effectivepre-reforming conditions including a pre-reforming temperature ofbetween about 300 and about 700° C. and a pre-reforming pressure ofbetween about 100 and about 350 kPa. More preferably, the pre-reformingtemperature ranges between about 350° C. and about 600° C., and mostpreferably the pre-reforming temperature comprises a temperature betweenabout 350° C. and about 550° C. The pre-reforming reaction is anendothermic reaction and requires heat be provided to initiate andmaintain the reaction.

In the present invention, the pre-reforming zone is in intimate thermalcontact with a first heat exchange zone which transfers heat by indirectheat exchange to the pre-reforming zone. The first heat exchange zone isheated by the passage of a burner exhaust stream or flue gas stream froma burner zone. It is an important aspect of the invention that theburner exit temperature of the burner exhaust stream not exceed about700° C. so that the heat transfer to the pre-reforming zone occur byconvection rather than by radiation. In this way, although there will besome loss of overall thermal efficiency, the first heat exchange zonecan be constructed of a material such as stainless steel or carbon steeland thereby avoid the use of exotic, high cost metallurgy in thepre-reformer zone. In order to maintain the burner exit temperaturebelow 700° C., the amount, or the rate, of the air stream passed to theburner zone is controlled. In this way the burner exit temperature setsthe maximum hot side temperature for the first heat transfer zone andmaintains the hot side temperature of the first heat exchange zone at arelatively constant level following the startup of the hydrogengeneration section and thereby avoids setting up a thermal cycle in thefirst heat exchanger and maintaining an essentially steady-statetemperature profile within the first heat exchanger. As used herein theterm steady-state means that the temperature profile is characterized bya lack of temperature transients. Also, by maintaining the burner exittemperature below the radiant heat transfer region, the use ofexpensive, sophisticated oxygen sensors and related controls andradiation shielding can be avoided.

The pre-reformed stream is passed at effective partial oxidationconditions to a partial oxidation zone wherein the pre-reformed streamis contacted with an oxygen-containing stream, or first air stream, inthe presence of a partial oxidation catalyst to produce a partialoxidation product. If the pre-reformed stream is not at effectivepartial oxidation conditions, such as during the startup of the fuelprocessor when there is insufficient fuel for the burner zone to heatthe pre-reforming zone, the pre-reformed stream and theoxygen-containing stream are ignited to begin the partial oxidationreaction in the partial oxidation zone. The partial oxidation productcomprises hydrogen, carbon monoxide, carbon dioxide and some unconvertedhydrocarbons. The partial oxidation catalyst is disposed in the partialoxidation zone as a fixed bed. Catalyst compositions suitable for use inthe catalytic partial oxidation of hydrocarbons are known in the art(See U.S. Pat. No. 4,691,071, which is hereby incorporated byreference). Preferred catalysts for use in the process of the presentinvention comprise as the catalytically active component, a metalselected from Group VIII noble metal, a Group IVA metal and a Group IAor IIA metal of the Periodic Table of the Elements composited on a metaloxide support, wherein the support comprises a cerium-containingalumina. The alumina can be alpha-alumina, or a mixture of alpha-aluminaand theta-alumina. Preferably the cerium is present in the amount ofabout 0.01 to about 5.0% by weight of the support. Preferably, the GroupVIII noble metal in the partial oxidation catalyst is a noble metalselected from the group consisting of platinum, palladium, and rhodium.Preferably, the Group IVA metal which is present on the partialoxidation catalyst is selected from the group consisting of germanium,lead, and tin and the Group IVA metal is present in an amount of fromabout 0.01% to about 5% by weight of the partial oxidation catalyst.Preferably, the Group IA or Group IIA metal is present in the partialoxidation catalyst is selected from the group consisting of sodium,potassium, lithium, rubidium, cesium, beryllium, magnesium, calcium,francium, radium, strontium, and barium and the Group IA or Group IIAmetal is present in an amount in the range of from about 0.01% to about10% by weight of the partial oxidation catalyst. The catalyticallyactive metal may also be supported on suitable carrier materials wellknown in the art, including the refractory oxides, such as silica,alumina, titania, zirconia and mixtures thereof. Preferably, the partialoxidation catalyst is granular and is supported as a fixed catalyst bedwithin the partial oxidation zone. In the process of the presentinvention, the partial oxidation zone is operated at effective partialoxidation conditions including a partial oxidation temperature of belowabout 1400° C. and a low partial oxidation pressure of between about 100and about 350 kPa. More preferably, the partial oxidation temperatureranges between about 500° C. and about 1400° C., and most preferably thepartial oxidation temperature is between about 600° C. and about 1100°C.

In the apparatus of the present invention, the partial oxidationreaction zone is positioned in close proximity to a steam reforming zoneso that the heat contained in the products of the exothermic partialoxidation reaction rather than being recovered is employed directly todeliver the partial oxidation effluent stream to the steam reformingzone at effective steam reforming conditions and to partially maintainthe steam reforming reaction zone at effective steam reformingconditions. In addition, the combined partial oxidation/steam reformingreaction zone links the exothermic partial oxidation zone with theendothermic steam reforming reaction zone to provide thermalcompensation for the high temperatures generated in the partialoxidation zone. The steam reforming zone provides internal cooling ofthe walls of the combined reactor zone thus permitting the use of carbonsteel and stainless steel metallurgy rather than exotic metallurgy in acombined partial oxidation zone/steam reforming zone. After starting upthe combined partial oxidation/steam reforming reactor arrangement,there is a need to switch from a partial oxidation mode towards a steamreforming mode of operation by reducing the air rate to the partialoxidation zone and by providing heat to the steam reforming zone. In theone embodiment of the present invention, additional heat is supplied bythe indirect heat exchange with the above mentioned burner exhauststream, or flue gas stream, so that during the operation of the combinedpartial oxidation/steam reforming reactor zone, the proportion of theconversion taking place in the partial oxidation zone is shifted infavor of the steam reforming zone. Preferably the flue gas temperatureranges from about 400 to about 800° C. This shift occurs as theincreasing anode waste gas supply and improving heating value permit theoperation of the burner zone to provide heat to the steam reforming zoneand the pre-reforming zone. The heating value or heating quality of theanode waste gas improves as the concentration of hydrogen in the anodewaste gas increases. In this manner the overall efficiency of the fuelprocessor can advance from the 77 percent energy efficiency of thepartial oxidation reaction toward the 87 percent energy efficiency ofthe steam reforming reaction. In this manner, the combined reactorsystem of the present invention approaches the higher efficiency of thesteam reforming operation, without the slow thermal and conversionresponse of the steam reforming zone. By overall efficiency it is meantthe percent efficiency as determined from the net heating value of thehydrogen in the product hydrogen gas divided by the net heating value ofthe feedstock. Once the system has reached operating temperatures, thatis the burner exit temperature and the steam reforming temperaturesapproach 700° C., these operating temperatures are maintained to retainthe essentially steady-state temperature profile in the first and thesecond heat exchanger zones and the variations in demand for electricalpower are met by switching between the partial oxidation and the steamreforming reactions and by adjusting the flow of the hydrocarbonfeedstock to the pre-processing, or preparation, module.

The use of partial oxidation provides improved start-up performancealthough it reduces the overall efficiency of the operation. Steamreforming on the other hand is slow to start up and operates at a muchhigher overall efficiency. The combination of the partial oxidation, thereforming, and the pre-reforming zones as provided by the presentinvention are especially useful in controlling and tolerating thefluctuations in the fuel rate as the demand for electrical power varies.Furthermore, the scheme employs a low complexity control system which isable to handle the variations in fuel flow rate and in fuel qualitysimultaneously.

The partial oxidation product is passed to the steam reforming zonecontaining a steam reforming catalyst to produce a reforming effluentstream. Preferably, the steam reforming catalyst includes nickel withamounts of noble metal, such as cobalt, platinum, palladium, rhodium,ruthenium, iridium, and a support such as magnesia, magnesium aluminate,alumina, silica, zirconia, singly or in combination. More preferably,the steam reforming catalyst can be a single metal such as nickel or anoble metal supported on a refractory carrier such as magnesia,magnesium aluminate, alumina, silica, or zirconia, singly or incombination, promoted by an alkali metal such as potassium. Mostpreferably, the steam reforming catalyst comprises nickel supported onalumina and promoted by an alkali metal such as potassium. The steamreforming catalyst can be granular and is supported as a fixed catalystbed within the steam reforming zone. In the process of the presentinvention, the steam reforming zone is operated at effective reformingconditions including a reforming temperature of below about 700° C. anda reforming pressure of between about 100 and about 350 kPa. Morepreferably, the reforming temperature ranges between about 350° C. andabout 700° C., and most preferably the reforming temperature is betweenabout 550° C. and about 650° C. The reforming effluent stream iswithdrawn from the reforming zone at a reforming exit temperature ofbelow about 700° C. The reforming exit temperature is maintained at avalue of about 700° C. by controlling the rate of the supply of theoxygen-containing stream to the partial oxidation zone. In this manner,the reforming exit temperature establishes the hot side temperature fora second heat exchange zone which will be employed to remove heat from awater gas shift reaction zone.

The reforming effluent is passed to at least one water gas shiftreaction zone which exothermically reacts the carbon monoxide over ashift catalyst in the presence of an excess amount of water to produceadditional amounts of carbon dioxide and hydrogen. The following is adescription of a two-zone water gas shift reaction zone, although anynumber of water gas shift reaction zones may be employed to reduce thecarbon monoxide level in the H₂ product. The steam reforming effluent iscombined with water and cooled to an effective high temperature shifttemperature of between about 400° C. to about 450° C. to provide acooled steam reforming effluent. The cooled steam reforming effluent ispassed over a high temperature shift catalyst to produce a hightemperature shift effluent. The high temperature shift catalyst isselected from the group consisting of iron oxide, chromic oxide, andmixtures thereof. The high temperature shift effluent is cooled toreduce the temperature of the high temperature shift effluent to atemperature of between about 180° C. and about 220° C. to effectiveconditions for a low temperature shift reaction and to provide a cooledhigh temperature shift effluent. The cooled high temperature shifteffluent is passed to a low temperature shift zone and contacted with alow temperature shift catalyst to further reduce the carbon monoxide andproduce a low temperature shift effluent. The low temperature shiftcatalyst comprises cupric oxide (CuO) and zinc oxide (ZnO). Other typesof low temperature shift catalysts include copper supported on othertransition metal oxides such as zirconia, zinc supported on transitionmetal oxides or refractory supports such as silica or alumina, supportedplatinum, supported rhenium, supported palladium, supported rhodium, andsupported gold. The low temperature shift reaction is a highlyexothermic reaction and a portion of the heat of the low temperatureshift reaction is removed by indirect heat exchange in a second heatexchange zone with a water stream to produce a steam stream. The steamstream is admixed with the treated hydrocarbon feedstock to furtherconserve thermal energy and provide steam to the pre-reforming zone. Thewater gas shift effluent stream or hydrogen product comprises less thanabout 0.5 mol-% carbon monoxide.

Because carbon monoxide acts as a poison to some fuel cells like the PEMfuel cell, the carbon monoxide concentration in the hydrogen productmust be removed, or its concentration reduced for example by oxidation,conversion, or separation, before the hydrogen product can be used inthese fuel cells to produce electricity. Options for post-processing ofthe hydrogen product stream to further reduce the carbon monoxidecontent include selective catalytic oxidation and methanation. Inaddition, some fuel cells operate at different levels of hydrogenconsumption per pass, or hydrogen efficiencies. For example, some fuelcell arrangements demand high purity hydrogen and consume more thanabout 80% of the hydrogen per pass, while others consume less than about70% of the hydrogen per pass and do not require high purity hydrogen. Ina case which requires high purity, the hydrogen product stream is passedto a separation zone comprising a thermal swing adsorption system or apressure swing adsorption system to produce a high purity hydrogenstream (95 to 99.999 mol-% hydrogen) and a separation waste streamcomprising carbon oxides. A portion of the high purity hydrogen streammay be used in the hydrodesulfurization zone and the remaining portionof the high purity hydrogen stream is passed to the fuel cell zone.Anode waste gas, along with the separation waste steam is passed to theburner zone. For non-fuel cell applications, the use of the anode wastegas can be substituted with a fuel gas stream such as a waste gas streamfrom a hydrogen purification system like a pressure swing adsorptionprocess.

For fuel cells such as PEM fuel cells which are sensitive to carbonmonoxide, the hydrogen product is passed to a carbon oxide oxidationzone at effective oxidation conditions and contacted with a selectiveoxidation catalyst to produce a carbon oxide reduced hydrogen productgas stream comprising less than about 40 ppm-mole carbon monoxide.Preferably, the carbon oxide reduced hydrogen product gas streamcomprises less than about 10 ppm-mole carbon monoxide, and morepreferably, the carbon oxide reduced hydrogen product gas streamcomprises less than about 1 ppm-mole carbon monoxide. The heat ofoxidation produced in the carbon monoxide oxidation zone is removed in aconventional manner by cooling the carbon monoxide oxidation zone in aconvention means such as with a water jacket and a cooling water stream.

For a PEM fuel cell, the carbon oxide reduced hydrogen product gascomprising water at saturation and at a temperature less than about 100°C. is passed to the anode side of a fuel cell zone comprising at leastone proton exchange membrane (PEM). The PEM membrane has an anode sideand a cathode side, and is equipped with electrical conductors whichremove electrical energy produced by the fuel cell when an oxygencontaining stream is contacted with the cathode side of the PEMmembrane. It is required that the PEM membrane be kept from drying outby maintaining the carbon oxide reduced hydrogen product stream atsaturation conditions. It is also critical that the PEM membrane bemaintained at a temperature less than 100° C. When the PEM membrane isoperated to be only about 70 percent efficient in its use of thehydrogen product stream, the fuel cell produces an anode waste gascomprising hydrogen and a cathode waste gas comprising oxygen.Typically, anode waste gas comprises hydrogen, nitrogen, and carbondioxide. The anode waste gas produced by the present invention comprisesless than about 50 mol-% hydrogen, and the cathode waste gas comprisesless than about 15 mol-% oxygen.

A second oxygen-containing gas such as air and the anode waste gaswithdrawn from the fuel cell anode side are contacted in the burner zonementioned hereinabove at effective combustion conditions to maintain aburner exit temperature less than about 700° C. In this manner, thehydrogen generated by the partial oxidation or steam reforming reactionzones and not consumed by the fuel cell is burned to provide thermalintegration of the overall process, and in the same burning step anynitrogen introduced by the use of the partial oxidation zone is therebyrejected.

In the configuration provided by the apparatus of the present invention,at a steady state operation there is no provision to add heat to thereforming step, and the degree of partial oxidation remains essentiallyconstant. The scheme is much more efficient than a fully autothermalprocess because the heat from the burner zone is used to provide heat tothe steam reforming reaction which raises the overall efficiency of theprocess. The use of the burner zone in intimate thermal contact with thereforming zone as employed in this scheme allows significantly more heatrecovery in the pre-reforming operation than if heat were only recoveredfrom the reaction products. Other schemes in the prior art only use heatrecovery from the reaction products, such schemes are most oftenpracticed in large-scale plants. The large-scale plants do not have ananode waste gas stream to employ as fuel. In addition, the process ofthe present invention permits the use of less exotic metals whichsignificantly reduces the capital cost of the key process equipment.

In the present invention when applied to fuel cell systems, only theanode waste gas is used as fuel, no methane is added and therefore nocomplex fuel balancing is required to manage fluctuations in fuelquality and anode waste gas production. Anode waste gas composition willvary both in amount and in heat capacity as the efficiency and demandfor electricity in the fuel cell change. The air flow to the burner zoneis controlled to compensate for the variations in the anode waste gascomposition and thereby achieve a constant burner exit temperature ofthe flue gas withdrawn from the burner. Thus, as the amount of heatavailable from the anode waste gas is reduced, reducing the heatavailable to the pre-reformer, there is a corresponding increase in theair demand or rate delivered to the partial oxidation zone to provideadditional heat to the system. In the partial oxidation zone a controlscheme is provided to control the outlet temperature of the reformer byvarying the amount of the second air stream that is introduced to thepartial oxidation zone. In this way, the steam reforming outlet, oreffluent temperature is maintained essentially at a constant value. Ifthe amount of anode waste gas decreases, the process begins to operateas an autothermal reforming process and the efficiency approaches about77 percent. If the anode waste gas heat content or amount increases theamount of partial oxidation is reduced. When the degree of partialoxidation is reduced, the overall process approaches a steam reformingoperation which has efficiency range between 85 and 87 percent.

Thermal variations in the apparatus and in the overall system areminimized to achieve a steady operation by the use of two independentburner control systems. By controlling the exit temperatures of theburner zone and the reforming zone in this manner, variations in thefuel rate are compensated for automatically to provide an essentiallysteady-state temperature profile in the external first and second heatexchange zones which eliminates thermal cycling within the individualheat exchange zones. In addition, the heat available to thepre-reforming zone, the partial oxidation, and the reforming zone alwaysachieve the same overall hydrocarbon conversion. Controlling thetemperature at the outlet of the reforming zone to a temperature ofabout 700° C. of permits the use of less exotic metallurgy in theconstruction of the apparatus for the partial oxidation and reformingzones and the coupling of the partial oxidation and steam reformingzones to any separate or additional heat exchange zone is not required.

One of the problems in developing hydrogen generation in small-scalereforming systems is the elimination of thermal cycling of the vessels.Such cycling can result in thermal stresses which lead to fatiguefractures at the welds. Variations in turndown rate, fuel rate, and fuelquality in prior art systems often resulted in a thermal cyclingthroughout the system. The control system disclosed herein maintains thehot side temperature profile in each of the major heat exchange zones atan essentially constant value after startup and thereby avoids anysignificant variation which would produce thermal cycling in the heatexchange zones. The cold side temperatures in the present system are setby the feed temperature. Thus, thermal cycling and the resulting damagefrom thermal stresses to heat exchanger zones are effectively limitedand an essentially uniform thermal profile is maintained within the heatexchanger zones. A feature of the process redistributes the heattransfer and reaction zones to employ heat exchange between streams withrelatively low thermal, or enthalpy, contents relative to the amount ofheat generated or consumed in the reaction zones. Variations in flowrates are controlled before these flow variations can impact theequipment and create temperature swings in the reaction zones. Thereby,temperature fluctuations in the heat exchanger zones are avoided.Furthermore, the present technique of the controlling hot sidetemperatures in a range which permits the use of less exotic metallurgywhile responding to fluctuations in electrical demand yields significantcapital cost advantages with a minimal loss of overall energyefficiency.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIG. 1, a hydrocarbon feedstock in line 1 for use in a fuelcell system for the generation electric power is passed to apre-reforming zone 14. A steam stream in line 8 is also passed to thepre-reforming zone 14. The pre-reforming zone contains a pre-reformingcatalyst selected from the group consisting of nickel on alumina, andthe like. The pre-reforming zone 14 is in intimate thermal contact witha first heat exchange zone 16 which supplies heat by indirect heatexchange in the convection temperature range to heat the pre-reformingzone 14. A pre-reforming effluent stream is withdrawn from thepre-reforming zone 14 in line 2. The pre-reforming effluent stream ispassed to a partial oxidation zone 24 at effective partial oxidationconditions including a partial oxidation temperature and a partialoxidation pressure. The partial oxidation temperature ranges betweenabout 550 and about 900° C. The partial oxidation pressure rangesbetween about 100 to about 350 kPa (15 to about 50 psia). Eithersimultaneously with the introduction of the pre-reforming effluent or asa partial oxidation feed admixture combined with the pre-reformingeffluent stream, a first air stream in line 4 is introduced to thepartial oxidation zone 24. The partial oxidation zone 24 contains apartial oxidation catalyst. In the partial oxidation zone, at least aportion of the pre-reforming effluent stream is converted to produce apartial oxidation effluent stream comprising hydrogen, carbon monoxide,carbon dioxide, and water. The partial oxidation effluent stream shownas line 3 is withdrawn from the partial oxidation zone 24 and passed toa reforming zone 28. The reforming zone 28 contains a reformingcatalyst. In the reforming zone 28, the partial oxidation effluentstream undergoes a further conversion to produce a reforming effluentstream comprising hydrogen, carbon monoxide, carbon dioxide, and water.The partial oxidation zone 24 and the main reforming zone 28 arecombined into a single combined reaction zone 26. The heat for thepre-reforming zone 14 is supplied by indirect heat transfer between fluegas from the burner zone 22. The heat from the reforming effluent streamwithdrawn from the reforming zone 28 is used to provide a steam streamin line 8 for the pre-reforming zone 14. The reforming effluent streamis withdrawn from the reforming zone 28 in line 5 and passed to a watergas shift reaction zone 18. The water gas shift reaction zone 18contains at least one water gas shift catalyst zone and provides for theconversion of carbon monoxide to additional amounts of hydrogen toproduce a hydrogen product stream. The hydrogen product stream iswithdrawn from the water gas shift reaction zone 18 in line 7. The watergas shift reaction is a highly exothermic reversible reaction and mustbe cooled to maintain the selectivity toward the conversion of carbonmonoxide and water to carbon dioxide and hydrogen. The water gas shiftreaction zone 18 of the present invention is cooled by indirect heatexchange with a second heat exchange zone 20 which is in intimatethermal contact with the water gas shift reaction zone 18. The water gasshift reaction zone 18 is used herein as a boiler and steam generationzone wherein a water stream in line 6 is passed through the second heatexchange zone to produce the steam stream in line 8. All or a portion ofthe steam stream in line 8 produced in this manner is returned to beadmixed with the hydrocarbon feedstock in line 1. In the apparatus ofthe present invention, the burner zone 22 is in intimate thermal contactwith the reforming zone 28 of a combined reaction zone 26 (See FIG. 1).

The hydrogen product stream in line 7 which generally comprises lessthan about 50 ppm carbon monoxide is passed to a fuel cell zone (notshown). If the fuel cell zone is sensitive to carbon monoxide, theconcentration of carbon monoxide may be further reduced in aconventional manner by selective oxidation techniques or methanationtechniques well-known to those skilled in the art. For example,reduction of the carbon dioxide concentration to a level of less than100 ppm-mol is required for PEM-type fuel cells, while carbonate basedfuel cell technology does not have a carbon monoxide limitation. In thefuel cell zone, the hydrogen product steam or a carbon monoxide reducedhydrogen stream is passed to an anode side of a fuel cell, while anoxygen containing stream such as air is passed to a cathode side of thefuel cell and an anode waste stream which is now depleted in hydrogenrelative to the hydrogen product stream is withdrawn from the fuel cell.The anode waste gas in line 9 and a second air stream in line 10, whichis introduced via line 10′ and valve V2 are admixed in line 9′ andpassed to a burner zone 22 to combust the anode waste gas and produce aflue gas stream in line 11. The burner zone may contain a combustioncatalyst to assure the complete combustion of the anode waste gas in theburner zone. The flue gas stream is passed to the first heat exchangezone 16 in line 11 to provide heat to the pre-reforming zone 14 and acooled flue gas stream is withdrawn from the first heat exchange zone inline 12.

In the operation of the process and apparatus for the generation ofhydrogen, the system is controlled in a relatively simple manner whichovercomes many of the problems associated with fluctuations in demandfor power and starting up the system. The control system for the processcomprises a temperature measuring device “T1” to measure the temperatureof the outlet of the reforming zone 28, shown as measuring the exittemperature of the reforming effluent in line 5, and adjusting the rateor flow of the first air stream in line 4′ by opening or closing valveV1. Initially at startup, the introduction of the first air stream ateffective partial oxidation conditions adds heat to the system byinitiating the exothermic partial oxidation reaction. The effectivepartial oxidation conditions are achieved at startup by heating thehydrocarbon/first air stream admixture with a heating means such as anelectrical heater. Microwave heating may also be employed to initiatethe partial oxidation reaction. The exit temperature of the reformingeffluent in line 5 is controlled by adjusting the rate of the first airstream. Increasing the rate of the first air stream increases the exittemperature and decreasing the air rate decreases the exit temperatureof the reforming effluent in line 5. As the reformer produces thereforming effluent, the reforming effluent is passed through the shiftreaction zone 18 and the fuel cell zone (not shown) and the anode wastegas in line 9 is mixed with the second air stream in line 10 andreturned to the burner zone to be combusted to produce the flue gasstream in line 11. The flue gas temperature in line 11 is measured bycontroller “T2” and the flow rate of the second air stream is adjustedto maintain the flue gas temperature below about 700° C. When the fluegas temperature is above the desired value, the rate of the second airstream is increased, and when the flue gas temperature is below thedesired value the rate of the second air stream is reduced. In thismanner the hot side temperatures of the heat exchange zones 16 and 20are maintained at relatively constant values and thermal cycling of theheat exchange surfaces is minimized.

FIG. 2 represents a system to be used in conjunction with the apparatusof the present invention for conversion of a hydrocarbon feedstock suchas a natural gas stream in line 30 , a liquefied petroleum (LPG) gasstream in line 32, or a gasoline boiling range stream in line 34 toelectric power E using a fuel cell. Referring to FIG. 2, a natural gasstream in line 30 is passed to a first pre-processing or preparationmodule 90 comprising a desulfurization zone. The desulfurization zonecontains a sorbent for the removal impurities such as sulfur compoundsincluding hydrogen sulfide and mercaptans. The desulfurization sorbentis selected from the group consisting of zeolites, activated carbon,activated alumina, zinc oxide, and mixtures thereof. A processed naturalgas stream is removed from the first pre-processing zone in line 31 andpassed via lines 31 and 40 to a fuel processor zone 93. The fuelprocessor zone comprises the components disclosed and described withrespect to FIG. 1 for the pre-reforming, partial oxidation, reforming,and burner processing operations and the first and second heat exchangeoperations to provide heat to the pre-reforming zone and to remove heatfrom the water gas shift reaction zone, respectively. A first air streamin line 42 is passed to the partial oxidation zone of the fuel processorzone 93, a second air stream in line 55 and an anode waste gas stream inline 54 are passed to the burner zone of the fuel processor zone 93, anda hydrogen product stream is withdrawn from the fuel processor zone 93in line 44. Depending upon the type of fuel cell system employed in thefuel cell 97, essentially 3 types of post-processing modules may beemployed, if any post processing is required. The degree ofpost-processing will also depend upon the hydrogen purity requirementsof the fuel cell 97. For example, if the fuel cell is designed toconsume less than about 70 percent; that is, the consumption of hydrogenper pass is between about 50 to about 75 percent, and the fuel cellrequires carbon monoxide reduction, then the hydrogen product is passedvia lines 44 and 45 to a selective oxidation zone 94 to catalyticallyoxidize the carbon monoxide to carbon dioxide and produce a processedhydrogen stream in line 46. The processed hydrogen stream is passed vialines 46 and hydrogen header 52 to the anode side 97 a of the fuel cell97. An oxygen stream such as a third air stream in line 56 is passed tothe cathode side 97 b of the fuel cell 97 to produce electric power.Similarly, a methanation zone 95, can be employed to reduce the carbonmonoxide concentration in the hydrogen product stream in line 44 bypassing the hydrogen product stream to the methanation zone 95 via lines44 and 47 and therein contacting the hydrogen product stream with amethanation catalyst at effective conditions well-known to those skilledin the art to produce the processed hydrogen stream in line 48, which isconveyed to the anode side 97 a of fuel cell 97 via the hydrogen header52. When the fuel cell 97 is designed to operate by converting at leastabout 80 mol-% of the hydrogen per pass, the hydrogen product stream ispassed via lines 44 and 49 to the post-processing module 96 which caninclude a pressure swing or a temperature swing adsorption step toproduce a high purity hydrogen stream in line 50. The high purityhydrogen stream comprises a hydrogen purity of greater than about 95percent hydrogen. As part of the pressure swing or the temperature swingadsorption step, a waste stream is produced at low pressure in line 57which is returned to the burner zone in the fuel processor zone 93. Theadvantage of using the pressure swing or the temperature swingadsorption step in post-processing module 96 is that the burner zoneoperation of the apparatus becomes more stable and waste gas and highpurity hydrogen are available as quickly as 20 seconds following thestart of operations. Catalytic operations such as those of the selectiveoxidation zone 94 and the methanation zone 95 require a 20 to 30 minutedelay before the catalytic zone can reach effective operating conditionsand any suitably treated product hydrogen stream is available. When thepressure swing or the temperature swing adsorption step is employed, aportion of the high purity hydrogen can be passed via line 50, hydrogenheader 52 and line 58 to provide a hydrogen stream to catalyticallydesulfurize a gasoline feedstock 34 in pre-processing module 92 whichcomprises a catalytic desulfurization zone and a sorbent desulfurizationzone. Shown in the drawing as line 58, a portion of the hydrogen productstream can be passed via lines 50, 52, and 58 to the desulfurizationzone (preprocessing module 92) to desulfurize the gasoline feedstock 34to provide a desulfurized gasoline feedstock in line 35 which can bepassed to the fuel processor zone 93 via lines 35 and 40. Thedesulfurization zone of pre-processing module 92 is similar to thedesulfurization zone of pre-processing module 90. The liquefiedpetroleum gas (LPG) stream in line 32 is generally essentially free ofsulfur having less than about 1 ppm-wt sulfur and the pre-processingmodule 91 comprises a pressure valve to reduce the pressure of the LPGto the pressure of the fuel processor system to pass the reducedpressure LPG in lines 33 and 40 to the fuel processor zone 93.

As shown in FIG. 3, the combined reaction zone apparatus 200 comprises avertically aligned reactor shell having a side-wall 235, a top head 202,and a bottom head 236. The side-wall 235 is insulated and defines aninterior reactor zone. The interior reactor zone has an upper shell zone212, a center shell zone 216, and a lower shell zone 233. A hollowcenter sleeve 209 is sealingly disposed on the top head 202 and extendsdownwardly into the lower shell zone 233. The hollow center sleeve 209has a hollow interior which defines an upper core zone 204, a centercore zone 211, and a lower core zone 213. A first oxidation catalyst isdisposed with the center core zone 211 or partial oxidation reactionzone. A porous particle retainer 203 is rigidly disposed in the uppercore zone 204 below the top head 202. An intermediate partition 237 issealingly disposed on the side-wall 235 in the center shell zone 216 andhas a downwardly converging diameter along its length and extendsdownwardly into the lower shell zone 233 encircling a portion of thehollow center sleeve 209. A burner zone 239 is defined within theinterior reactor zone outside of the intermediate partition. Theintermediate partition 237 may be welded or sealingly disposed to theside-wall 235. A reforming zone 215 is defined within the interiorreactor zone inside the intermediate partition 237. The lower core zone213 is in fluid communication with the reforming zone 215. A reformingcatalyst is disposed above the bottom of the intermediate partition 237in the reforming zone 215 and in the lower core zone 213. A top annularscreen 217 is rigidly disposed between the side-wall 235 and theintermediate partition 237 in the burner zone 239. A bottom annularscreen 219 is similarly disposed in the burner zone below the topannular screen 217. The bottom annular screen 219 is rigidly supportedby an outer and an inner support ring (221, 220). The outer support ring221 is rigidly disposed on the side-wall 235 and the inner support ring220 is rigidly disposed on the intermediate partition 237 in the lowershell zone 233. A feed inlet nozzle 201 is disposed on the top head 202in fluid communication with the upper shell zone 212. A product outletnozzle 231 is disposed on the side-wall 235 or the top head 202 in fluidcommunication with the upper shell zone 212. A burner feed nozzle 223 isdisposed on the side-wall 235 or on the bottom head 236 in fluidcommunication with the lower shell zone 233 in the burner zone 239. Anexhaust nozzle 229 for exiting flue gas is disposed on the side-wall 235in fluid communication with the burner zone 239. An igniter 205 extendsthrough the top head 202 and downwardly through the porous particleretainer 203 well into the center core zone 211. Preferably, the igniter205 extends to a point near the middle of the center core zone 211. Theigniter 205 is removably disposed through the top head 202 and theporous particle retainer 203. The igniter 205 is comprised of two rodshaving a proximal end and a distal end. The rods comprise an alloy suchas incoloy and are bridged by at least two cross bars or other bridgingmeans for electrically bridging the rods at the distal end. The rods arepositioned inside the center core zone or partial oxidation reactionzone 211 such that when sufficient electrical current is applied to theproximal ends of the igniter rods, there will be heat transferred to thepartial oxidation catalyst in an amount which is effective to light-offthe partial oxidation reaction.

In the combined reaction zone apparatus 200, a first oxidation catalystis disposed in the center core zone 211. A reforming catalyst isdisposed in the lower core zone 213 and in the reforming zone 215. Asecond oxidation catalyst is disposed in the lower shell zone 233between the top and bottom annular screens (217, 219). Optionally, afirst layer of inerts is disposed above the first oxidation catalyst inthe upper core zone 204. A second layer of inerts 214 is disposed in theupper shell zone 212 above the reforming zone 215. A third layer ofinerts 227 is disposed below the top annular screen 217 and above thesecond oxidation catalyst 225. The inert layers above the catalyst serveto support the catalysts during the assembly of the combined reactionzone apparatus 200 and to improve fluid distribution and heat transferwithin the combined reaction zone apparatus 200.

The combined reaction zone apparatus 200 is shown which includes thefunctions of a partial oxidation zone 211, a reforming zone 215, aburner zone 239, a first internal heat transfer zone between the exhaustgases and the reforming zone and a second internal heat transfer zonebetween the partial oxidation zone 211 and the reforming zone 215. Thepartial oxidation zone 211 serves to provide heat to the reforming zone215 and the heated reforming zone provides heat to ignite the burnerzone 239. Thus, the apparatus includes two burner zones (211 and 239)wherein the first burner zone 211 provides heat to light the secondburner zone 239 without the need for an igniter in the second burnerzone. The first burner zone comprises the partial oxidation zonecontaining a first oxidation catalyst and the second burner zonecomprises the burner zone. A second oxidation catalyst 225 is preferablydisposed in the burner zone 239 to assist in the combustion of gases inthe burner zone. In the burner zone 239, a fuel gas or a waste gas suchas anode waste gas from the fuel cell zone is essentially completelycombusted.

At startup, partial oxidation feed or the effluent from thepre-reforming zone is introduced into the partial oxidation reactorinlet 201 and passed into a partial oxidation reaction zone 211 formedby the interior of the center sleeve. The partial oxidation feed passesthrough a bed of inert material in the upper core zone 204. The inertmaterial can include ceramic balls, silica, glass, or quartz. Thepartial oxidation feed contacts the partial oxidation catalyst in thecenter core zone 211. This bed of inert material serves to place thepartial oxidation zone in the center of the combined reaction zoneapparatus 200 and provides a thermal offset which permits less exoticmetals such as stainless steel to be used in the construction of thecombined reaction zone apparatus. A partial oxidation catalyst found tobe particularly useful for oxidizing methane at a low light-offtemperature is a catalyst prepared from alpha-alumina having about 1wt-% platinum and having a reduced acid activity. The acidity of thepartial oxidation catalyst is reduced by the further addition of about0.35 wt-% lithium on the alpha-alumina.

EXAMPLES Example I

The operation of a fuel processor of the present invention was simulatedwith an engineering design and simulation system for the conversion of anatural gas stream at ambient temperature into electric power using aPEM fuel cell wherein the anode waste stream withdrawn from the fuelcell is the only source of fuel to heat the pre-reforming zone. The fuelprocessor is designed to produce about 130 NL/mn of hydrogen to beconverted into about 10 kW (net production about 7 kW) of electricityfrom the fuel cell using about 70% of the hydrogen per pass. Within thesystem, the exit temperature of the combined partial oxidation/reformingzone is maintained at about 650° C. and the temperature of the flue gasleaving the burner zone is maintained at about 650° C. by controllingthe rate of the first and second air streams passed to the partialoxidation/reforming zone and the burner zone, respectively.

In the scheme for processing natural gas, the natural gas at a flow rateof about 2.07 kg/h and a pressure of about 1.3 kPa is passed to acompressor to raise the pressure to about 86 kPa and a temperature ofabout 80° C. to provide a compressed feed stream. The compressed feedstream is passed to a treater containing zinc oxide and operating atdesulfurization temperature of about 250° C. to remove sulfur impuritiesand to produce a treated feed stream. The treated feed stream is passedto a pre-reforming zone which contains a pre-reforming catalyst and isheated by the flue gases from a burner zone such that the pre-reformingeffluent stream is maintained at a pre-reforming effluent temperature ofbetween about 400° and 650° C. The pre-reforming effluent comprisesabout 40 mol-% hydrogen, 19.2 mol-% methane, 1.2 mol-% CO, 7.6 mol-%CO₂, 0.6 mol-% N₂ and about 31.4 mol-% H₂. The pre-reforming effluent ispassed to a combined partial oxidation zone/reforming zone and thesecond air stream is introduced at a second air rate to maintain theexit temperature of the reforming zone at or below 650° C. About 6.5kg/h of air are combined with about 6.54 kg/h pre-reforming effluent toproduce a reforming effluent of about 13.04 kg/h. The reforming effluentcomprises about 39.1 mol-% H₂, 22.2 mol-% H₂₀, 1.1 mol-% methane, 7.8mol-% CO₂, 7.0 mol-% CO, and about 22.8 mol-% N₂. The effluent is passedto a shift converter which is cooled by indirect heat exchange with anionized water stream to produce a steam stream and a shift effluentstream. The shift effluent stream comprises 45.66 mol-% H₂, 22.8 mol-%nitrogen, 14.36 mol-% CO₂, 15.6 mol-% H₂O, and about 0.5 mol-% CO.

The shift effluent stream or product hydrogen stream is passed to apreferential oxidation (prefox) zone for the further reduction of the COcontent of the product hydrogen stream to less than about 50 ppm-mol CO.A prefox effluent stream is withdrawn from the prefox zone at atemperature of about 80° C. The prefox effluent or CO reduced hydrogenproduct stream, or “prefox” effluent is passed to the anode side of thefuel cell to produce about 10.4 kW of electric power and an anode wastegas stream. The fuel cell uses about 70% of the hydrogen and produces ananode waste gas stream. Approximately 1 to 1.6 kW of power are consumedby the compressor and an air blower second air stream is introduced at asecond air rate to maintain the exit temperature of the reforming zoneat or below 650° C. About 6.5 kg/h of air are combined with about 6.54kg/h pre-reforming effluent to produce a reforming effluent of about13.04 kg/h. The reforming effluent comprises about 39.1 mol-% H₂, 22.2mol-% H₂O, 1.1 mol-% methane, 7.8 mol-% CO₂, 7.0 mol-% CO, and about22.8 mol-% N₂. The effluent is passed to a shift converter which iscooled by indirect heat exchange with an ionized water stream to producea steam stream and a shift effluent stream. The shift effluent streamcomprises 45.66 mol-% H₂, 22.8 mol-% nitrogen, 14.36 mol-% CO₂, 15.6mol-% H₂O, and about 0.5 mol-% CO.

Example II

The process disclosed herein permits the heat exchangers and combinedreactor apparatus components of the fuel processor to operate within thetemperature and pressure limitations of carbon steel and stainless steelwhich significantly influences the total cost of the fuel processorapparatus. The following Table presents the relative cost of the fuelprocessor apparatus as a function of the materials of construction. Byoperating the fuel processor such that the hot side of the process doesnot exceed 700° C., either stainless steel or carbon steel can beemployed resulting in significant savings over operating in thereforming reactors and combustion zones in the radiant heat exchangeregion to achieve high heat exchange efficiencies and using exoticmaterials. The following Table presents the relative cost of the fuelprocessor apparatus as a function of the materials of constructionrelative to the cost of all carbon steel materials. The process as shownin FIG. 1 when operated to maintain the reforming exit temperature andthe burner flue gas temperature below 650° C., permits the use of carbonsteel or stainless steels for all of the heat exchanger and reactorapparatus components of the system. Surprisingly, this high sidetemperature limitation results in a significant cost advantage for theoverall system. For example, according to the cost ratio for the use ofincoloy, there is a 12:1 cost advantage for the carbon steel materialsand a 2-3:1 advantage for use of the stainless steel materials (304 or316) over the use of incoloy.

TABLE RELATIVE COST OF FUEL PROCESSOR EQUIPMENT Max. Allowable MaterialTemperature Stress Cost Carbon Steel 900° F. 6500 psi 1 2-¼ Cr - 1 Mo1200° F. 1400 psi 3 9 Cr - 1 Mo 1200° F. 1500 psi 6.55 304 S.S. 1500° F.1400 psi 3.95 316 S.S. 1500° F. 1300 psi 5.7 321 S.S. 1500° F.  300 psi6 347 S.S. 1500° F.  800 psi 7.8 Incoloy 800H 1650° F.  980 psi 11.9 HK40⁴ 2000° F.  800 psi 16.3

We claim:
 1. A combined partial oxidation burner reactor comprising: avertically aligned reactor shell having a top head and a bottom head,and side-wall defining an interior reactor zone, said interior reactorzone having an upper shell zone, a center shell zone, and a lower shellzone; a hollow center sleeve sealingly disposed on the top head andextending downwardly into the lower shell zone, said center sleevehaving a hollow interior defining an upper core zone, a center corezone, and a lower core zone; an intermediate partition having adownwardly converging diameter along its length sealingly disposed onthe side-wall in said center shell zone encircling a portion of saidhollow center sleeve, said lower core zone being in fluid communicationwith a portion of the center shell zone located within said partition; aburner zone defined within the interior reactor zone between the bottomhead and said intermediate partition; a feed inlet nozzle disposed onsaid top head in fluid communication with the upper core zone; a productoutlet nozzle disposed on said reactor shell in fluid communication withsaid upper shell zone; a burner feed nozzle disposed on said reactorshell in fluid communication with the burner zone; an exhaust nozzledisposed on said reactor shell in fluid communication with the burnerzone; and an igniter extending through the top head and downwardly intothe center core zone; wherein a first oxidation catalyst is disposed insaid center core zone and a reforming catalyst is disposed on theintermediate partition in the center shell zone and in the lower corezone.
 2. The combined partial oxidation burner reactor of claim 1further comprising a first layer of inerts disposed above said firstoxidation catalyst.
 3. The combined partial oxidation burner reactor ofclaim 1 further comprising a second layer of inerts disposed on saidreforming catalyst in the upper shell zone.
 4. The combined partialoxidation burner reactor of claim 1 further comprising: a top annularscreen disposed in the burner zone and rigidly disposed between theside-wall and the intermediate partition in the burner zone; and abottom annular screen disposed in the burner zone, said bottom annularscreen rigidly supported by an outer and an inner support ring, saidouter support ring being rigidly disposed on the side-wall and the innersupport ring being rigidly disposed on said intermediate partitionwithin the burner zone; wherein a second oxidation catalyst is disposedbetween the top and bottom annular screens.
 5. The combined partialoxidation burner reactor of claim 3 further comprising a third layer ofinerts disposed above said second oxidation catalyst.
 6. The combinedpartial oxidation burner reactor of claim 1 wherein said side-wall, tophead, bottom head, center sleeve, and intermediate partition comprisestainless steel.
 7. The combined partial oxidation burner reactor ofclaim 1 wherein said partition is welded to the side-wall.
 8. Thecombined partial oxidation burner reactor of claim 1 wherein saidigniter comprises two rods each having a proximal end and a distal endextended into the center core zone wherein said rods are bridged by atleast two cross bars at the distal end.
 9. The combined partialoxidation burner reactor of claim 1 wherein said igniter is removablydisposed through said top head.
 10. The combined partial oxidationburner reactor of claim 1 further comprising a porous particle retainerrigidly disposed in the upper core zone within the center sleeve.